The present invention relates to a workpiece transporting device of the magnetically floating type suitable for use in a semiconductor fabrication system or the like, under a under vacuum condition.
Generally, a semiconductor wafer is treated within a vacuum chamber during the semiconductor fabrication process. The semiconductor wafers and other workpiece articles are handled by a transporting device within the vacuum chamber. Therefore, the transporting device is required to be free of dust during the course of the transporting operation. FIG. 6 shows an example of the conventional transporting device used under the vacuum condition. In the figure, a multi-chamber 1 is comprised of a plurality of processing rooms 2-4, a loading room 5 and an unloading room 6, the rooms being arranged around a central area of the chamber 1. A turntable 8 is disposed on the central area of the chamber 1. A transporting device 10 of the magnetically floating type is mounted on the turntable 8. This transporting device 10 has an arm 11 movable in the lengthwise or axial direction of the device. A server is provided at an end portion of the arm 11 for carrying a semiconductor wafer 13.
In such a multi-chamber, the semiconductor wafer 13 is charged and discharged into and from respective processing rooms 2-4, loading room 5 and unloading room 6 during the course of the fabrication process. For this handling, the turntable 8 is rotated to place the server of the arm 11 in front of a desired room, and then the arm 11 is extended or retracted to charge or discharge the semiconductor wafer 13 into or from that room. In this operation, it is necessary to check to see if the semiconductor wafer 13 is being carried on the server in order to ensure the correct fabrication process. However, there is no practical article sensor which is reliable in the vacuum. Therefore, conventionally an optical sensor is provided outside the multi-chamber 1 so as to detect the presence or absence of the semiconductor wafer 13. In order for the optical sensor to view the interior of the multi-chamber from the exterior thereof, a quartz glass piece 14 is fitted in an opaque top plate 15 in registration with a sensor (not shown in the figure).
However, such a multi-chamber 1 is costly since a plurality of the quartz glass pieces 14 must be fitted into the top plate 1. Further, each sensor must be addressed sequentially in synchronization with a position shift of the semiconductor wafer 13 during the course of the semiconductor fabrication process. A detection sequence of the sensors is provisionally set, but this complicated sequence is occasionally set erroneously to thereby cause a check miss.